1. Field of the Invention
The present invention relates to a method and apparatus for connecting a wire from an existing wire supply to a wire from a new wire supply during manufacturing of a wiring harness. The invention also relates to a method and apparatus for detecting a wire joint.
2. Description of the Related Art
A prior art wiring harness requires a plurality of wires of a specified lengths. The wires are drawn from a plurality of wire supplies to a cutting/mounting apparatus where the respective wires are cut to the specified lengths. Terminals then are crimped or otherwise connected to the cut ends of the wires. It is often necessary to change the wire that is being processed. To make this change, the wire drawn from a first wire supply is cut. A wire from a second wire supply then is connected with the cut end to enable a continued production of the wiring harness.
Several wire connection methods have been known and/or used in the prior art. One prior art wire connection method inserts the ends of the wires into a sleeve and compresses the sleeve to connect the wire ends. However, the compression force or the crimping force of the sleeve sometimes is insufficient. Accordingly the reliability of this connection method is low. Additionally, the sleeve is expensive.
A second prior art wire connection method welds the wire ends together, as disclosed in Japanese Unexamined Patent Publication No. 8-138824. However, this prior art method is expensive, and the finishing of the joint portion is unstable. More particularly, burrs and/or flash may be formed. Flash, in particular, may disadvantageously clog the nozzle through which the wire is fed.
A third prior art wire connection method successively feeds crimping pieces by a strip, positions the wire ends to be connected on the crimping piece along a straight line, crimps the crimping piece into a tubular shape, and cuts the crimping piece from a carrier piece, thereby connecting the wire ends by crimping. This prior art method requires the difficult step of positioning and abutting the ends of the wires against each other. Additionally burrs are likely to be formed if the wire ends overlap, and the burrs are likely to catch the nozzle.
A fourth prior art wire connection method winds an aluminum tape over and around the both wire ends to connect the wires. However the aluminum tape is expensive, and typically must be wound by hand, thereby causing poor operability and low connection reliability.
A fifth prior art wire connection method strips sheaths of the wire ends to expose strands and twists or braids the exposed strands to connect the wire ends. The twisting or braiding of the strands at both wire ends can be difficult to achieve. This operation is difficult to automate, and hence generally is done by hand. Manual operations of this type cause a poor operability and low connection reliability.
The manufacturing of a wiring harness requires a specified length of wire to be drawn from a wire supply and further requires terminals to be mounted on both ends of the cut wire by crimping, insulation displacement, etc. A prior art wire cutting/crimping apparatus is used for this purpose. A wire joint detecting apparatus is provided in a wire running path that extends from the wire supply to the wire cutting/crimping apparatus. The wire joint detecting apparatus detects the presence of a wire joint and cuts off the section of wire with a wire joint so that a product includes no wire joint.
The wire joint generally is formed by twisting exposed conductors. As a result, the wire joint typically is detected by applying a voltage to a pair of opposite untwisting rollers 1 (1a, 1b in FIG. 15) that are provided along a running path of a wire “a”. More particularly, the rollers 1a, 1b are connected electrically via the wire joint when the exposed conductors of the wire joint pass between the rollers 1a, 1b. Thus the electrical connection of the rollers 1a, 1b detects the wire joint. A detection error can occur if there is a defective contact between the wire “a” and the rollers 1a and 1b. Additionally the wire joint cannot be detected unless the conductors are exposed.
Other prior art apparatus has detected the wire joint by a color sensor that detects the tape used in the prior art for joining wires. The detection by the color sensor does not require the conductors to be exposed. However, the sensor itself is expensive, it is difficult to adjust the sensor for detection and an erroneous detection frequently is made.
In view of the above, an object of the present invention is to provide a wire connecting method and apparatus, which have high connection reliability and which can be automated easily.
It is also an object of the invention to provide a wire joint detection method and apparatus for reliably allowing a detection of a wire joint regardless of whether the conductors are exposed at the wire joint.